1. Field of the Invention
The present invention relates to a method of manufacturing a thin film transistor array substrate. Some embodiments use a reduced number of mask processes.
2. Description of the Related Art
Thin film transistor array substrates are used in many display devices including for example liquid crystal displays. A liquid crystal display device displays an image by using an electric field to control optical properties of liquid crystal material. The liquid crystal display device includes a liquid crystal display panel which has liquid crystal cells arranged in a matrix. The liquid crystal panel is driven by a driving circuit.
The liquid crystal display panel includes a thin film transistor array substrate and a color filter array substrate facing each other. The liquid crystal material is located between the two substrates. A spacer is located between the two substrates to maintain a desired cell gap between the two substrates.
The thin film transistor array substrate includes gate lines and data lines, thin film transistors used as switching devices at least one of which is located at every crossing of a gate line with a data line, pixel electrodes connected to the respective thin film transistors wherein each pixel electrode substantially defines the location of a liquid crystal cell, and an alignment film. The gate lines and the data lines receive signals from the driving circuit through suitable contact pads. A scan signal supplied to a gate line turns on the respective thin film transistors to supply the respective pixel electrodes with pixel voltage signals carried by the respective data lines.
The color filter array substrate includes color filters formed to correspond to the liquid crystal cells, a black matrix for reflecting external light and optically separating the color filters from each other, a common electrode for supplying a reference voltage to the liquid crystal cells, and an alignment film.
The thin film transistor array substrate and the color filter array substrate are manufactured separately, and then attached to each other. The liquid crystal material is then injected between the two substrates, and then the edges around the substrates are sealed.
Fabrication of the thin film transistor array substrate involves semiconductor processes and in particular mask processes. Each mask process typically includes a lithographic (selective) exposure of a material sensitive to some radiation, e.g. photolithographic exposure of photoresist using for an optical mask such as a quartz mask with a chrome pattern, or electron beam exposure or some type of exposure. Each mask process further includes cleaning, deposition of photoresist or other sensitive material, stripping of the sensitive material, inspection and the like. The mask processes complicate the manufacturing and are a major factor in the manufacturing cost. Consequently, reducing the number of mask processes is a common goal in manufacturing. Manufacturing processes are known which use five mask processes to manufacture a thin film transistor array substrate. More recently the number of mask processes has been reduced to four.
Further reduction of the number of mask processes is desired.